Just to give my take real quick:
Even from down here on Earth, with all of the pollution, galaxies that are millions of light-years away can occasionally be seen, such as the Andromeda. The fact that there is no light left in that void whatsoever, even viewing it from up in space, means we can deduce it at LEAST reached out of the Milky Way galaxy, and possibly even other galaxies. The thing is, we don't have confirmation that there were galaxies in its path. It's fully plausible, hell it could even warrant a possibly or likely on the pages I would say. But without confirmation, it is still technically speculative, and thus the safest way to go would be 4-A.