Global stock markets took a battering Monday after Greece shuttered its banks for the week and imposed limits on cash withdrawals — developments that have reinforced fears the country is heading for a debt default and a messy exit from the euro. Investors are fretting about the uncertainty posed by the events in Greece. Though many experts say the global economy — even Europe — is in better shape to withstand a potential Greek exit from the euro, some point out that its implications are not fully clear. Stocks fell in Asia and Europe, where Germany’s main index was down 3.5 percent and Greece’s market remained closed for the week. The euro fell sharply, as did oil prices, and Wall Street was expected to open lower.