If you have your listing defaults set to domestic shipping only, *AND* you have the setting in the "Buyer requirements" section "Block buyers who have a primary shipping address in a location I don't ship to" set, you should not get any international bids or purchases.
You may still get purchases from international buyers who have merchandise shipped to U.S. addresses or use third-party intermediaries, however for your purposes, those are considered domestic shipments, as your obligation is to confirm delivery only to the U.S. destination as specified in the payment.
EDIT: I just saw that you are located in the United Kingdom. While my post was written with U.S. eBay
in mind, presumably the same settings and restrictions exist on UK eBay