Do I need a transit visa for Moscow Domodedovo airport?

If you are planning to stay within the airport transit area for 6 hours the you definitely don't need the transit visa. If you are planning to go outside of the airport than you do need the transit visa. I would strongly advise against going outside of the airport if you want to see the city. The airport is pretty far from the city, the traffic is ridiculous, if you wander off you might miss your flight. Unless you planning to quickly take a glimpse of the Red Square and Kremlin and hop back to get to the airport, get the visa.