Assuming the flights connect at DME, see the airport's website on connections. The same applies for transit through SVO.

No Russian visa is required if you don't leave the international transit area. If you do, or have to switch airports you need some sort of visa. You will probably have to show the airline taking you to Moscow the reservation for the continuing flight to show you're not entering the country.

If you do arrive at DME and depart from SVO, you're in for a world of hurt. You'll need a transit visa and allow many hours to do the transfer. I only bring this up because IAH-Moscow implies the Singapore Air flight which arrives at DME. However, there are no non-stops from DME to Beijing, so either you connect in another city, or you're leaving from SVO which does have nonstops to Beijing.