YAHOO.util.Get.autopurge

// autopurge, bool,  If true, script nodes will automatically be removed every 20
// transactions (configurable via YAHOO.util.Get.PURGE_THRESH property. 
// Default: true for script nodes, false for CSS nodes.
YAHOO.util.Get.PURGE_THRESH = 5;
YAHOO.util.Get.script(aURLs, {
    onSuccess: successHandler,
    autopurge: true
});