I was unfamiliar with that theory, so I googled it.
WMAP Cosmology 101: Big Bang Concepts
So, here is how I understand it. Correct me if I am off on some of the details.
We do not know whether the universe is finite or infinite. Whether it is one or the other depends on whether the density of the universe is more of less than a certain critical density.
If less, then the gravitational pull of our universe's matter is not sufficient to wrap itself into a ball, and our universe is infinite. This would mean, even taking dark matter into consideration, there may be a vacuum somewhere out there in infinity that does not contain dark matter.
If the density of our universe is greater than, or equal to, the critical density, then the gravational pull of our universe's matter is strong enough to wrap itself into a sphere or some sort of half torus looking shape, which would mean our universe is finite and much less likely to contain a vacuum somewhere without dark matter.
My money is riding on a finite universe, purely for esoteric reasons. One of the seven Hermetic Laws --- the Law of Correspondence [As Above, So Below. As Below, So Above] --- would predict that the macrocosm of the universe would be spherical, as is the microcosm of the sun and the earth, as is the microcosm of the the electron "shell" that surrounds an atom. Also, some esoteric systems teach there are multiple universes, which inherently presumes that each universe is finite.
But, wait. We haven't yet stirred into the mix the very real possibility, suggested by the math of theoretical physicists, that our universe is actually ten-dimensional instead of three-dimensional plus time plus space. But, if that is the case, we might as well just throw our hands in the air now and concede that only a Divine Intelligence would have the capacity to grasp the intricate details of the Real.