same deal with US citizens with residence permission outside USA. the degree to which they pursue it depends on the bounty they will get from it. tax agencies are extortionists, in a government suit costume. the cost of extraction is proportional to the per-extraction minimum cost. so if you are under it, they won't chase you, even within so-called US federal jurisdictions. "catch me outside, how bout dat" is the first rule of dealing with punk asses like this. if you have enough to be worth chasing you can probably find a thousand ways to dodge them.