Facebook caches already shared urls/pages for better performance. This causes issues at time when we update the title, picture being shared or the description of the page because facebook still shows the older version of the page.
How to clear Facebook Share caches?
Facebook has a developer tool called Debugger. This tool gives us an idea about how a url will be shared on Facebook, ...posted on Jun 03, 2012
Author: Peter Malis, Freshshare Blog