esatto ecco il form :

function cancellamess(){

document.forms["mess"].message.value="";

}
function scrolling(){
window.setTimeout("cancellamess()", 1000);
}

<form name="mess" id="mess" method="post"
action="pagina.php" target="ISC"><input type="text" style="width:100%;" name="message" /><input type="submit" value="" onclick="scrolling()" style="visibility:hidden;" /></form>