The invention, and still more the dissemination, of the stirrup is closer in time to Genghis Khan than to the early Indo-European cultures, though.
The big question is of course whether Alexander the Great's famous hetairoi used stirrups or not. According to [0] they're considered among the first shock cavalry, and yet I can't find anything about them using stirrups, so clearly mounted combat, including shock cavalry, must have been possible without them.