diff --git a/releasenotes/notes/cache-scan-all-branches-a935824a844d1d9f.yaml b/releasenotes/notes/cache-scan-all-branches-a935824a844d1d9f.yaml
new file mode 100644
index 0000000..0102507
--- /dev/null
+++ b/releasenotes/notes/cache-scan-all-branches-a935824a844d1d9f.yaml
@@ -0,0 +1,6 @@
+---
+features:
+  - |
+    The ``reno cache`` command and ``build_reno`` setuptools command now
+    default to scanning to all enabled branches. This ensures the cache is
+    complete for projects that use multiple branches, such as stable branches.
diff --git a/reno/cache.py b/reno/cache.py
index 20c2a8e..326bae6 100644
--- a/reno/cache.py
+++ b/reno/cache.py
@@ -10,6 +10,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import collections
 import os
 import sys
 
@@ -21,7 +22,14 @@ from reno import scanner
 
 def build_cache_db(conf, versions_to_include):
     s = scanner.Scanner(conf)
-    notes = s.get_notes_by_version()
+
+    branches = [conf.branch]
+    if not conf.branch:  # if no branch requested, scan all
+        branches += s.get_series_branches()
+
+    notes = collections.OrderedDict()
+    for branch in branches:
+        notes.update(s.get_notes_by_version(branch))
 
     # Default to including all versions returned by the scanner.
     if not versions_to_include:
diff --git a/reno/scanner.py b/reno/scanner.py
index da7f88a..d1dca86 100644
--- a/reno/scanner.py
+++ b/reno/scanner.py
@@ -810,7 +810,7 @@ class Scanner(object):
         "Return true if the file exists at the given commit."
         return bool(self.get_file_at_commit(filename, sha))
 
-    def _get_series_branches(self):
+    def get_series_branches(self):
         "Get branches matching the branch_name_re config option."
         refs = self._repo.get_refs()
         LOG.debug('refs %s', list(refs.keys()))
@@ -846,7 +846,7 @@ class Scanner(object):
         if branch.startswith('origin/'):
             branch = branch[7:]
         LOG.debug('looking for the branch before %s', branch)
-        branch_names = self._get_series_branches()
+        branch_names = self.get_series_branches()
         if branch not in branch_names:
             LOG.debug('Could not find branch %r among %s',
                       branch, branch_names)
@@ -910,7 +910,7 @@ class Scanner(object):
                 return candidate
         return None
 
-    def get_notes_by_version(self):
+    def get_notes_by_version(self, branch=None):
         """Return an OrderedDict mapping versions to lists of notes files.
 
         The versions are presented in reverse chronological order.
@@ -918,13 +918,13 @@ class Scanner(object):
         Notes files are associated with the earliest version for which
         they were available, regardless of whether they changed later.
 
-        :param reporoot: Path to the root of the git repository.
-        :type reporoot: str
+        :param branch: The branch to scan. If not provided, using the branch
+            configured in ``self.conf``.
         """
 
         reporoot = self.reporoot
         notesdir = self.conf.notespath
-        branch = self.conf.branch
+        branch = branch or self.conf.branch
         earliest_version = self.conf.earliest_version
         collapse_pre_releases = self.conf.collapse_pre_releases
         stop_at_branch_base = self.conf.stop_at_branch_base
@@ -967,7 +967,7 @@ class Scanner(object):
             # On the current branch, stop at the point where the most
             # recent branch was created, if we can find one.
             LOG.debug('working on current branch without earliest_version')
-            branches = self._get_series_branches()
+            branches = self.get_series_branches()
             if branches:
                 for earlier_branch in reversed(branches):
                     LOG.debug('checking if current branch is later than %s',
diff --git a/reno/tests/test_cache.py b/reno/tests/test_cache.py
index abf19a2..5d158d4 100644
--- a/reno/tests/test_cache.py
+++ b/reno/tests/test_cache.py
@@ -12,6 +12,7 @@
 # License for the specific language governing permissions and limitations
 # under the License.
 
+import collections
 import fixtures
 import textwrap
 
@@ -24,10 +25,15 @@ from reno.tests import base
 
 class TestCache(base.TestCase):
 
-    scanner_output = {
-        '0.0.0': [('note1', 'shaA')],
-        '1.0.0': [('note2', 'shaB'), ('note3', 'shaC')],
-    }
+    scanner_output = [
+        collections.OrderedDict([  # master
+            ('0.0.0', [('note1', 'shaA')]),
+            ('1.0.0', [('note2', 'shaB'), ('note3', 'shaC')]),
+        ]),
+        collections.OrderedDict([  # stable/1.0
+            ('1.0.1', [('note4', 'shaD')]),
+        ]),
+    ]
 
     note_bodies = {
         'note1': textwrap.dedent("""
@@ -42,7 +48,11 @@ class TestCache(base.TestCase):
         'note3': textwrap.dedent("""
         features:
           - We added a feature!
-        """)
+        """),
+        'note4': textwrap.dedent("""
+        fixes:
+          - We fixed all the bugs!
+        """),
     }
 
     def _get_note_body(self, filename, sha):
@@ -57,12 +67,18 @@ class TestCache(base.TestCase):
         self.c = config.Config('.')
 
     @mock.patch('reno.scanner.Scanner.get_notes_by_version')
-    def test_build_cache_db(self, gnbv):
-        gnbv.return_value = self.scanner_output
+    @mock.patch('reno.scanner.Scanner.get_series_branches')
+    def test_build_cache_db(self, mock_get_branches, mock_get_notes):
+        mock_get_notes.side_effect = self.scanner_output
+        mock_get_branches.return_value = ['stable/1.0']
         expected = {
             'notes': [
-                {'version': k, 'files': v}
-                for k, v in self.scanner_output.items()
+                {'version': '0.0.0',
+                 'files': [('note1', 'shaA')]},
+                {'version': '1.0.0',
+                 'files': [('note2', 'shaB'), ('note3', 'shaC')]},
+                {'version': '1.0.1',
+                 'files': [('note4', 'shaD')]},
             ],
             'file-contents': {
                 'note1': {
@@ -77,6 +93,9 @@ class TestCache(base.TestCase):
                 'note3': {
                     'features': ['We added a feature!'],
                 },
+                'note4': {
+                    'fixes': ['We fixed all the bugs!'],
+                },
             },
         }
 
@@ -85,4 +104,7 @@ class TestCache(base.TestCase):
             versions_to_include=[],
         )
 
+        mock_get_branches.assert_called_once()
+        mock_get_notes.assert_has_calls([
+            mock.call(None), mock.call('stable/1.0')])
         self.assertEqual(expected, db)
diff --git a/reno/tests/test_scanner.py b/reno/tests/test_scanner.py
index 5c7a794..297188c 100644
--- a/reno/tests/test_scanner.py
+++ b/reno/tests/test_scanner.py
@@ -2432,7 +2432,7 @@ class GetSeriesBranchesTest(Base):
         self.scanner = scanner.Scanner(self.c)
         self.assertEqual(
             [],
-            self.scanner._get_series_branches(),
+            self.scanner.get_series_branches(),
         )
 
     def test_real_branches_sorted_names(self):
@@ -2445,7 +2445,7 @@ class GetSeriesBranchesTest(Base):
         self.scanner = scanner.Scanner(self.c)
         self.assertEqual(
             ['stable/a', 'stable/b'],
-            self.scanner._get_series_branches(),
+            self.scanner.get_series_branches(),
         )
 
     def test_eol_tag(self):
@@ -2455,7 +2455,7 @@ class GetSeriesBranchesTest(Base):
         self.scanner = scanner.Scanner(self.c)
         self.assertEqual(
             ['stable/a'],
-            self.scanner._get_series_branches(),
+            self.scanner.get_series_branches(),
         )
 
     def test_mix_tag_and_branch(self):
@@ -2468,5 +2468,5 @@ class GetSeriesBranchesTest(Base):
         self.scanner = scanner.Scanner(self.c)
         self.assertEqual(
             ['stable/a', 'stable/b'],
-            self.scanner._get_series_branches(),
+            self.scanner.get_series_branches(),
         )