As I attempted to go to the source today, I discovered that in May Jeff Davis left Microsoft to pursue other opportunities. Having retrieved the mini-FAQ from the Google cache, it is copy/pasted below for preservation purposes. The simplest solution is just to use Delete Browsing History (on the Tools menu) to clear the cache and the history store.
Q: I put a really is an icon, but it still doesn't appear.
If you are setting the no-cache directive for the icon file, then IE will not be able to display your icon and will display the default icon instead. Q: How do I create a different tag and point to a different filename than you previously used.I have this annoying problem in IE where it is displaying the wrong favicons (the little icons next to the URL and on the browser tab).So when I am on Google, it will show the icon for Stumble Upon, or something else. Some sites display the wrong icons in the address bar and favorites list. The only way I can clear the problem is to reset IE8 to its default settings.