Sorry, I don't have a very good reference for early Irish coins. The only book I have that covers them is my old copy of Friedberg's "British World" catalogue, which lumps all three kings together into a single listing. Spink/Seaby has issued a "Coins of Ireland" catalogue, and a "Scotland, Ireland & Channel Islands" catalogue, both of which which would probably tell you what you wanted to know - if anyone in fact knows for sure.
You probably already know, but I can tell that it's CIVITAS DVBL... - Dublin mint.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis