The name DOMINGUE, and the alternative spelling DOMAINGUE, also exist on the island Mauritius, in the Indian Ocean.The island is predominantly french speaking (although the official language is English) and so the original pronounciation of the name has not been lost.
I therefore concur with the 'Do-mang'/rhymes with meringue descriptions.
Mauritius itself has a population of just over one million and is about 60 miles by 40 miles in size. Major industries are suger, textiles and tourism. Also famous as where the Dodo used to live.
My ancestors emmigrated there from France variously in the 1700s and 1800s.I was born there, but have lived most of my life in the UK.