A writ of garnishment, whether issued in a case of attachment or on a judgment or decree, shall be served as a summons is required by law to be executed; but if the garnishee be not personally served, and make default, judgment nisi shall be rendered against him, and a scire facias awarded, returnable to the next term, unless the court be satisfied that the garnishee can be personally served at once, in which case it may be returnable instanter.