Back button on browser caches instead of reloading entire page in php web application

Happy Wednesday Experts!

I have a website, where there is an alert which has code as below

 @if (\Session::get('message')<>'')
    <script>
        window.onload = function ()
        {
          message = 'Success message';
          $.notify(message, {timeout: 3000,pos: 'top-right'});
        }
    </script>
    @endif

Now, It is working perfectly. After I submit, I get a message from code behind "Success message" and now I moved to a different page. It is loaded without any problem. I decided to click on back button of browser and I see that success message. It shows the Alert message (success message) .

Could someone help me with this?

After show message, before moving any other page, I already cleared session message.

I believe I have something to do with caching and postbacks but not sure how or what to do