The Benchmark domestic equity indices, Sensex and Nifty, were trading marginally down in the afternoon trade today amid mixed global cues. The 30-share BSE Sensex dropped 140 points to 81,191 and the NSE Nifty50 slipped 21 points to 24,646, when reports last came in. Earlier, both the indices had opened with minor cuts as selling was seen in index heavyweights.