You have to counterfile, but there's a poison pill in the regulation that by doing so you agree U.S. courts have jurisdiction, thereby nullifying any protections you have from being in another countries juridiction.

I mean, there is no getting around it if you want the countersuit to work and reflect poorly on the claimant, but you are agreeing to letting the U.S. have extra-territorial jurisdiction.

If you're in the US then you're already under jurisdiction, right? Why wouldn't someone who is already under us jurisdiction try it?

Huh? If you aren't in the US you can ignore DMCA entirely.

In practice most hosting companies will suspend your server until you remove whatever was claimed against.