You can put parent grid refresh code after onAfterSave event of subgrid code.
$grid[“onAfterSave”] = “function(){ jQuery(‘#list1’).trigger(‘reloadGrid’,[{jqgrid_page:1}]); }”;
where list1 is parent grid id.
Code: http://phpgrid.org/demo/demos/master-detail/subgrid_detail.phps Line 118