According to this,
https://en.wikipedia.org/wiki/Intergalactic_star
Rogue stars are theorized to be the intergalactic space because of this,
The way these stars arise is still a mystery, but the most common theory is that the collision of two or more galaxies can toss some stars out into the vast empty regions of intergalactic space.
Could a planet be toss from a galaxy just like it's theorized rogue stars are?