That's a great question. I can recall from my international business classes that the US taxes the profit that American corporations make throughout their foreign subsidiaries as soon as they bring the money back into the country. This helps to reduce tax-haven chicanery. Generally speaking, in EU there're lower taxes (due to the economy situation most of european countries are favoring FDI).
However, potential tax liability might apply: there are countries outside EU the US does not have an income tax treaty with; Even when a treaty does exist, certain countries sill require tax filings to obtain treaty benefits.
I'd recommend you to look at the EU law in general and at the regulations in the specific country (even though if in a community, laws are different from country to country).