User blog comment:FairyRaven/Fairy Tail Chapter 352: The Flame's Voice, Review and Commentary/@comment-86.66.207.123-20130920112307/@comment-7418318-20130920115000

While it's gramatically possible that the dark magic is going to purify something, it'd be a rather unusual way to say so.

More likely the title means that the dark magic will be purified (i.e. purged) by something/someone.

Though maybe the title was intentionally left ambiguous. Japanese has many ways to keep things ambiguous, which makes it great for word-games, but hard to translate at times, since in the western languages you can't have this ambiguity and have to decide on one of the possible meanings when translating.