> Especially, if your domain is older than the trademark.

My understanding is that trademarks are about the term being recognised "in common", while a ® is once you pay money to your govt's department for the fancy paper. Hence, if you registered <cool name>.com and sold said cool named game, you already have a trademark simply because you're the author. (Of course, money for lawyers and proving things in court isn't free, but you have legal grounds to stand on nonetheless.)