Owin MicrosoftAccount doesn't appear to SignOff

I'm using Owin authentication for users authenticating to a Microsoft account.  When the user logs out, the security cookies do not seem to get removed or expired (not sure what Owin does under the covers).  I searched for solutions to this problem and found many people who are experiencing the same issue, their solutions don't appear to work for me however.
My Startup.Auth.cs contains the following to initialize the Microsoft account provider:
app.SetDefaultSignInAsAuthenticationType(CookieAuthenticationDefaults.AuthenticationType); app.UseCookieAuthentication(new CookieAuthenticationOptions { }); // Uncomment the following lines to enable logging in with third party login providers var msOwinAuth = new Microsoft.Owin.Security.MicrosoftAccount.MicrosoftAccountAuthenticationOptions { ClientId = ConfigurationManager.AppSettings["Microso ...