SSO Logout with product SSO

Summary

Not actually logged out of SSO with product SSO

Content

We just setup Product SSO and my IT guy is concerned with the security of the logout process. I have a LOGOUT link in the header code and it appears to work fine; click Log Out and return to the learncenter homepage. 

<span id="loginState"><a href="https://sso.mycompanyname.com/auth/logout?returnto=http://www.mycompanyname.com/learncenter">LOGOUT</a></span></strong></div&gt;

However, if I click the back arrow, it will return to me being logged in. If I was securely logged out of SSO, it should NOT return me to a logged in state without actually logging in again. Is this a Microsoft SSO issue? What is everyone else who is using product SSO doing to get around this security issue?