TCERs (Test Case Execution Records) show the context of execution based on test plan, iteration, and test environment.  So if you navigate to the desired test plan using Planning > Browse Test Plan and then the Test Case Execution section, you will see a table with all the execution records.  You can then group them by Test Environment using the "Group by" drop-down, or use the Inline Filter to filter for just the environments you want.  The Last Result column will tell you what has been run or what hasn't.