I'm the SO. For the record, we both totally realize there is no hard or actual border, per se. Question came up as an idle curiosity ("hey, wouldn't it be neat to get a pizza delivered TECHNICALLY Internationally"), and even though it seemed like a bit of a silly question to both of us, we tried to look it up on Domino's app. Domino's does seem to be a bit weird and strict in a lot of place about their delivery - we live less than 8km from our local shop, and they will deliver within .5km of me, but not to my house because it is JUST across the town line. But they will happily deliver to houses that are much farther away than I am, as long as they are in the right post code!

As my example when I was testing on the app, I actually tried to see if I could get a pizza delivered to Bridgend (exactly where the first commenter talked about, in fact) from the Domino's just across the border in Derry. Although the Domino's in Derry was only about 5km away, it was instead directing us to the Domino's in Letterkenny, which is more like 25km - and that made it seem like crossing the border was a big deal for Domino's at least! Suspect that it's because it's a big corporation, though, as opposed to a smaller shop which would probably be less likely to care? Also can't help but wonder if we called the Domino's in Derry on the phone if they would actually do it, even though the app says no - there may just be programming limitations with the app that strictly forbid it from allowing orders across the border, even if it's feasible to do so.