How does the CACHE Table ever get purged? It just grows and grows?

Also when I get the DMLReceiveItem Event how do I refresh just the
one record that I'm on? I've tried InvalidateBookmark and this just
removes the record from my dataset. I'm using CachedUpdates and
don't really have a choice to not at this point. All the articles I
read say to just use the invalidatebookmark. What am I doing wrong?

Thanks,

Matt