The multiversal destruction isn't something Davros can pull off on his own.
Davros's Reality Bomb apparently uses technobabble physics to define some waveform which eliminates all matter, and his plot was to build a multi-planet engine that continuously produced such a wave to destroy everything but the Daleks. Allowing that there's probably a universe in which Davros was allowed to construct and trigger such a device - and there probably was, given we see an alternate timeline where the stars start going out in Turn Left - it doesn't appear to cross over into the Doctor's universe at all.
The plot in Journey's End however, takes place in the Medusa Cascade, a bent-up region of space that contains a rift allowing Davros to spread the annihilation wave through all possible realities (or so he says). We know that all possible realities includes the parallel world (Pete's World) Rose got trapped in from Doomsday, because the Doctor is able to drop her off there when all is said and done with Davros. We don't know if Davros is really able to back up his claims though - reality hopping isn't well quantified other than the Doctor mentioning it was easier to do when Gallifrey ran everything. Certainly Davros intended to force the rift as wide open as he could to wipe out plenty of everything, and certainly more than one universe would have been destroyed. Rifts have two side though, and the Doctor has made a habit of closing them wherever he can (except Cardiff, apparently).
So if there is a bleak pocket of nowhere in the multiverse where a version of Davros has succeeded in turning on a Reality Bomb, and also having a rift handy nearby to throw it through... it has likely been stopped from affecting the Doctor's universe by sealing the Medusa Cascade rift from this side once our Davros was stopped.
