we have an ico file in our etc/designs/ pathing. We've updated this image and attempted to flush the cache by the following
activating /etc/design/foo tree
activating page which uses this image
de-activating and re-activating a number of pages
the image is properly in the publish environment but the dispatcher contiues to cache.
The dispatchers are set up correctly and we do get pages that are modifed to clear the cache correctly.
Check http://helpx.adobe.com/cq/kb/HowToFlushAssetsPublish.html. Basically on publish modification events are fired only for pages. Can you try to adapt the workaround listed there?