A320 flight crew experience a dual FMGC failure on initial climbout and return to their departure station for repairs.

Narrative

During initial climbout; FMGC #2 appeared to partially fail. First Officer's map went away on his Navigation Display and had to match his range distance to Captain's side. Attempted to reset FMGC #2 about 4 times per Quick Reference Handbook procedures with no change. Sent an ACARS message to Dispatcher as to legality of crossing Gulf of Mexico with only 1 FMGC. Maintenance told Dispatcher to have us return to ZZZ (they remotely had queried the aircraft and determined that both FMGCs were not working correctly). Both FMGCs were replaced in ZZZ; tested; flight then completed. Note: Quick Reference Handbook guidance is so confusing that it's of no operational value. Quick Reference Handbook addresses 'FMGC failure dual (2).' What is being addressed here? A Dual FMGC Failure? They why the '1' or '2' in parenthesis? Or do these address a single FMGC failure (1) or (2)? We need very specific guidance in our Quick Reference Handbook to identify a single FMGC failure. How are we to proceed operationally; i.e.; can we continue into 'waters' airspace or conduct CAT II/III approaches? We also need very specific guidance to address a dual FMGC Failure; since the aircraft goes virtually 'nil automation' in such a situation. Our current Quick Reference Handbook pages are so confusing that we weren't even sure if they applied to our situation.