http://www.mobilitywod.com/2011/07/episode-283-resetting-after-a-shoulder-tweakbrutally-sore-shoulders/

Also try putting a lacrosse ball underneath your infraspinatus while lying on your back and bringing your arm through internal rotation with your arm bent at a 90 degree angle. This will help loosen up the upper back muscles like the infraspinatus that are responsible for external rotation.