How to update facebook open graph image

Say if you have set the facebook image for your webpage via the meta tag of the open graph protocol like this: <meta property="og:image" content="http://ia.media-imdb.com/rock.jpg"/>

If you want to replace/update the image with another image of the same name rock.jpg, how do you get facebook to update your image accordingly with the new image when you share the page? Forcing facebook to fetch your page's data with this link http://developers.facebook.com/tools/debug won't update the image.