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.
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"Time is what prevents everything from happening at once" - John Wheeler