As we know, rogue planets don't orbit around a star, how about galaxy? Can a rouge planet not orbit around a galaxy?
They would be enormously difficult to observe, but with a big enough gravitational assist a rogue planet certainly could be ejected from a galaxy and become a "double rogue" so to speak, or intergalactic rogue planet is probably a better term. Rogue (or intergalactic) stars have been observed. Here and Here. The same gravitational forces that create intergalactic stars absolutely should create inter-galactic rogue planets and in fairly significant numbers. The merging of 2 galaxies should create millions of them.
There is no reason why it couldn't, though the chances of it happening are small. There are hyper velocity stars that are not gravitationally bound to the Milkyway, if a planet is ripped away from its star due to a close encounter with another star or black hole it could be given enough velocity to reach a galaxies escape velocity (about 537 km/s).