diff --git a/mercurial/debugcommands.py b/mercurial/debugcommands.py
--- a/mercurial/debugcommands.py
+++ b/mercurial/debugcommands.py
@@ -1478,7 +1478,8 @@ def debugmanifestfulltextcache(ui, repo,
     if opts.get(r'clear'):
         with repo.lock():
             cache = getcache()
-            cache.clear()
+            cache.clear(clear_persisted_data=True)
+            return
 
     if add:
         with repo.lock():
diff --git a/tests/test-manifest.t b/tests/test-manifest.t
--- a/tests/test-manifest.t
+++ b/tests/test-manifest.t
@@ -142,3 +142,9 @@ Accessing the initial entry again, refre
   id: 1e01206b1d2f72bd55f2a33fa8ccad74144825b7, size 133 bytes
   id: fce2a30dedad1eef4da95ca1dc0004157aa527cf, size 87 bytes
   total cache data size 268 bytes, on-disk 268 bytes
+
+Check cache clearing
+
+  $ hg debugmanifestfulltextcache --clear
+  $ hg debugmanifestfulltextcache
+  cache empty