A default judgement requires that a case be filed. In the US, that means they have to serve you notice of the case.

Obviously they have the OP's address, so if they fail to serve him the judgement should be easy enough to set aside.

I'd do absolutely nothing in this circumstance until and unless they actually initiate a legal proceeding. If they did sue for the domain, depending on the value of brand I probably lawyer up, and perhaps seriously consider counter-suing them for both their domain and the use of the business name itself.