If you are working on your single entry blog and notice when shared via FB network it is getting incorrect thumbnail image. Then you change it, but when shared it is still using same image or text.

There is a quick fix to clear the cache:

https://developers.facebook.com/tools/debug/

Then enter your URL, it will put there the time of caching, but you can renew it by clicking on the button next to time. This way FB will see the new changes at your site.