diff --git a/diigo-cache/README.md b/diigo-cache/README.md
index 57a777e..9b4a409 100644
--- a/diigo-cache/README.md
+++ b/diigo-cache/README.md
@@ -44,7 +44,9 @@ goal 2 preamble).
 - **Fill job**: walks every diigo page into a cache in the background —
   DO alarms, a few pages per step, progress stored in the DO
   (`startFill`/`fillStatus`/`stopFill`), driven from the webkey page;
-  the public page shows progress.
+  the public page shows progress. "Invalidate the last N days" there
+  drops the cached pages holding anything updated that recently
+  (`invalidateRecent`), so the next fill refetches them.
 - The `DiigoBridge` entrypoint for other workers (its cache-id source is
   the goal-2 wiring TODO).