4. Switch to another workspace.  At this point Emacs thinks neither
   frame is visible (I'm guessing they're all iconified).  I know this
   because in my customised compilation-finish-functions I do a
   notifications-notify for long-running compilations, but only if the
   compilation BUF does not satisfy (get-buffer-window BUF 'visible).

5. Switch back to the workspace with Emacs.

6. Repeat steps 2-3.