Marchi, it's been found that the distribution of galaxies coincides with the distribution of Dark Matter, according to a study published in Nature journal a few years ago. The supposed reason is the gravitational attraction of 'ordinary' matter toward dark matter. That doesn't mean there's no Dark Matter in the cosmic cavities that you mention. I imagine there is. But the view at the moment is that most of it's in the same regions as most of the ordinary matter.
"Time is what prevents everything from happening at once" - John Wheeler