In a parallel universe, the Borg homeworld was located in the Delta Quadrant. After breaking their alliance with the Borg, the Cybermen set a course for the Borg homeworld in order to take complete control of the Borg Collective. Ultimately, however, they were defeated before reaching their goal by the combined forces of the Eleventh Doctor, the USS Enterprise-D, and surviving Borg. (COMIC: Assimilation²)
Behind the scenes
Officially, the existence of a Borg homeworld is a hypothetical one as it has yet to be revealed in a canon Star Trek source. However, an identity for the Borg homeworld is given by the novel Lost Souls, which names it Arehaz.