My original answer read as thus. However, thereThe designation galactic cluster was complaintjust that it did not answer the original question. And furtherA designation. While a comment that itgalactic cluster is a area comprised of hundreds to thousands of galaxies, galactic cluster 3 was notmerely a good answerdifferent phase of already known space to the borg. SoAs was the fluidic space of galactic cluster 8, I will takeknown for the fluidic space of species 8472. The only time to elaborateanyone has gone outside of the Milky Way galaxy was by aid of "The Traveler" from TNG.
Original Post
The designation galactic cluster was just that. A designation. While a galactic cluster is a area comprised of hundreds to thousands of galaxies, galactic cluster 3 was merely a different phase of already known space to the borg. As was the fluidic space of galactic cluster 8, known for the fluidic space of species 8472. The only time anyone has gone outside of the Milky Way galaxy was by aid of "The Traveler" from TNG. Amended
The Borg have not, under any official canon ever left the Milky Way Galaxy. For those of you that do not follow, or have no looked up the term "galactic cluster" mentioned previously by Seven of Nine, in the above posts; A galactic cluster is a group of hundreds to thousands of star systems held together by gravitational pull. When referenced in Star Trek however, it was an inaccurate portrayal, as the Borg merely used the term to describe the space coexisting in a parallel plane or dimension of space. Galactic Cluster 3, as mentioned by Seven of Nine was the Borg designation for a transmaterial energy plane intersecting 22 billion omnicordial lifeforms.
The Borg encountered Species 259 in Galactic Cluster 3. They assimilated autonomous regeneration sequencers from this species, a technology later installed by the Borg aboard the USS Voyager in 2374. (VOYAGER:"The Gift")
Memory Alpha describes a galactic cluster as a type of "Spatial Domain". Given that this is the "only" reference to what might be considered intergalactic travel within the canon information in Star Trek with relation to the Borg, it becomes clear that the only way that it could be construed as being intergalactic is; if you count the spatial domain entered as being in a separate galaxy. Which without any evidence to support it, we very well can not. This includes Galactic Cluster 8. The fluidic space of species 8472.
In conclusion; no. The Borg have never (by canon) traveled outside of the Milky Way Galaxy. The only known beings to travel intergalactically were the crew of the Star Ship Enterprise 1701-D with the aid of the "Traveler" who was skilled in his ability not for his racial abilities. But instead, due to what he claimed to be a higher level of thought. With his aid, the Enterprise traveled to the Triangulum Galaxy, (over 3 million Light years away. and later to the "End of the Universe" a billion light years from the Milky Way Galaxy. (TNG: Where No One has Gone Before)
