If you will ship some products abroad and only ship other products domestically, then the only way to do that is by having two separate E-junkie accounts for US-only vs. Worldwide products.
Since items from two different accounts cannot be added to a common cart (which you wouldn't want anyway -- e.g., what happens when a buyer adds a combination of US items and Worldwide items to the same order if they're not in the US?), you should probably also keep the US-only products on a completely separate site, or in their own subsection of your own site apart from the Worldwide products, so it wouldn't be likely for a buyer to wander back and forth between the two sites or subsections.