diff --git a/lisp/progmodes/project.el b/lisp/progmodes/project.el
index 599a350e5ce..9cc70335afc 100644
--- a/lisp/progmodes/project.el
+++ b/lisp/progmodes/project.el
@@ -193,6 +193,10 @@ project-find-functions
   'project-current-directory-override
   "29.1")
 
+(defvar project-forget-functions (list #'project-vc-forget-directory)
+  "Special hook to clear cache for a directory tree.
+Each function on this hook is passed a string, the directory file name.")
+
 (defvar project-current-directory-override nil
   "Value to use instead of `default-directory' when detecting the project.
 When it is non-nil, `project-current' will always skip prompting too.")
@@ -599,6 +603,13 @@ project-try-vc
           (vc-file-setprop dir 'project-vc project)
           project))))
 
+(defun project-vc-forget-directory (root)
+  (obarray-map
+   (lambda (sym)
+     (when (string-prefix-p root (symbol-name sym))
+       (vc-file-setprop (symbol-name sym) 'project-vc nil)))
+   vc-file-prop-obarray))
+
 (defun project--submodule-p (root)
   ;; XXX: We only support Git submodules for now.
   ;;
@@ -1875,6 +1886,7 @@ project-forget-project
 PROJECT-ROOT is the root directory of a known project listed in
 the project list."
   (interactive (list (funcall project-prompter)))
+  (run-hook-with-args 'project-forget-functions project-root)
   (project--remove-from-project-list
    project-root "Project `%s' removed from known projects"))
 
@@ -1999,6 +2011,8 @@ project-remember-projects-under
 projects."
   (interactive "DDirectory: \nP")
   (project--ensure-read-project-list)
+  ;; Clear the cache for DIR and below, in case of prior visit.
+  (run-hook-with-args 'project-forget-functions dir)
   (let ((dirs (if recursive
                   (directory-files-recursively dir "" t)
                 (directory-files dir t)))