The Sensex at the Bombay Stock Exchange declined 101 points, or 0.5 percent, to close at 21,033, on profit-booking by investors, amid falling global markets, today. The Nifty at the National Stock Exchange fell 31 points, or 0.5 percent, to 6,242.Stock markets in Japan, Hong Kong, South Korea and Singapore lost between 0.2 percent and 3 percent.