If you don't own it anymore... why would you care????
If you do own it, get ready to lose it.. BUT! Alot of these don't go anywhere. Here's why.
The people complaining have to have one (or more) of the following three things in order to win:
1) Court Order (but if you were never served, you can fight this if the $$$ are worth it).
2) Registered Trademark (Note, REGISTERED Trademark, you can check this out at uspto.gov)
3) Registered Copyright (Note, REGISTERED, you can check this out at uspto.gov)
Now, it your domain name was something like procterandgamble.com your screwed.. But if it's a local enterprise who never properly trademarked, etc. you've got a fighting chance.
But always make sure your evaluating and making a good Business Decision. How much money is it worth, cost of distraction, etc. before doing anything.
Then again, since you used to own it, it most likely isn't any of your business anyway.