How to refresh image on Page's wall?

We have been sharing links to our website on our Page's wall. Facebook correctly grabs a thumbnail of the main image of the link we're using, however, that main image has since changed and we'd like to be able to refresh Facebooks cache to use that new image.

On our website, I've already tried adding a "?fbrefresh=1" parameter to the end of the (img /) tag and I've also completely changed the (img /) source to a different image, all to no avail.

How can I update or refresh Facebooks cache?

Hello,

I believe Facebook grabs the thumbnail from the site when the link is posted. When try to post the link now, does the main page update itself?