Recently, the hubs and I tried a tip from pintrest, to soak your stove grates in ammonia to remove the built on grease and gook. It certainly worked well on the pieces of our stove. So well, the hubs decided to try it on caked on cookie sheets.
I'll let the pictures do the talking here.
Before - yes those were my cookie sheets! Clean, just baked on caked on gook!
Here's my take on it - it did remove all of that gook and crap, but I also think it removed the non-stick coating - which I OK I don't really care too much about that. Just wash them really well with soap and water, maybe even running through the dishwasher when you're done!