At risk of sounding facetious - it's slightly different, being brown in colour rather than red. The idea is pretty much the same, though. I had a friend from south of the border who asked the same thing and was convinced that we were probably talking about the same thing, until I brought a bottle of the Belfast variant back after a trip home. Funnily enough, after a ferret of the interweb, I can't find any pics to illustrate the difference.

Has to be said, I'm not all that surprised that you didn't come across it, since it's not one of those things that you'll find being served in bars - you'll find it in shops, though. I think that the creeping march of Coca-Cola capitalism probably means that its days are numbered in any case.

Probably worth asking your mum if she remembers it.