This is might be known to every one who worked on facebook integration with their site. That is, facebook is providing a tool for checking Open Graph protocol is correct or not and also for checking the access token is still valid or not. This tool also reset the cache of our page.
If we integrate Facebook Like or Share with our websites, we might need to change our code frequently. So expectations is we will see immediately the reflection on Facebook for our changes. But Facebook caches the pages when it comes for the first time to our Websites. And may be the cache period is 24 hour. So we have to wait 24 hour to see that my correction or changes are working as expected or not. NO! There is a tool provided by facebook at : http://developers.facebook.com/tools/debug. This tool provide us the feature as when we give our page URL and press Debug button it resets the cache. And also it shows the Open Graph objects are declared correctly or not.
So, hope from now on we don't need to wait until the facebook reset their cache we will be able to find Open graph problem very easily.