DEBUG FLUSHCACHE needs to wait that everything was synched on disk

src/debug.c

@@ -182,6 +182,9 @@ void debugCommand(redisClient *c) {
             addReplyError(c, "DEBUG FLUSHCACHE called with diskstore off.");
             return;
         } else {
+            /* To flush the whole cache we need to wait for everything to
+             * be flushed on disk... */
+            cacheForcePointInTime();
             emptyDb();
             addReply(c,shared.ok);
             return;