How can I clear the code coverage and I'm stuck to 60% and regardless its not what test I write its not increasing but my question is: is there a way to flush the cache?
You can clear your coverage in Setup > Develop > Apex Test Execution > View Test History > Clear Test Data. Afterwards, you can go to Setup > Develop > Apex Classes, and choose Run All Tests to regenerate your coverage.
The other way I found is just going to this url and will take you what sfdcfox talking about: hope this will help others.
Make sure you change XYZ with whatever Salesforce instance