1. A processing unit, comprising: a memory; an arithmetic logic unit; and control logic having access to program instructions of a control store, said control logic comprising logic to: access multiple scopes of variables by a scope index, variables in the different scopes of variables being identically referenced by instructions; associate at least one of the scopes of variables as a current scope of variables to be used in instructions that are executed by the arithmetic logic unit using the scope index; automatically change the scope index in response to a procedure call; automatically change the scope index in response to a procedure exit; and alter a value of a variable of a scope of variables other than the scope of variables associated with the current scope of variables in response to an instruction.