User blog comment:Omega natsu2/Chapter 364: Tartarus Arc, Part 1: Immorality and Sinners, Predictions./@comment-4449950-20131214020850/@comment-4829046-20131214073037

Well technically it is said to nullify magic all across the continent not the world. So if there are wizards in other parts of the world(islands) then that's not really that grand.