use following code after logout page.
function DisableBackButton() {
changeHashOnLoad()
}
DisableBackButton();
window.onload = DisableBackButton;
window.onpageshow = function (evt) { if (evt.persisted) DisableBackButton() }
window.onunload = function () { void (o) }
function changeHashOnLoad() {
window.location.href += "#";
setTimeout("changeHashAgain()", "50");
}
function changeHashAgain() {
window.location.href += "1";
}
var storedHash = window.location.hash;
window.setInterval(function () {
if (window.location.hash != storedHash) {
window.location.hash = storedHash;
}
},
50);