Issue on CodeIgniter

Hello sir

while working on project , I have found an issue, in a project A there is two different portal say B and C. 

When I need to logout from C then it should be logout from B also and vice-versa.
Similarly if we don't want to logout from b , then how to handle such situation.   Currently, I am stuck in this situation.
In reality, in my case project A contain 8 portal    . So how to handle such situation. Even If I am routing to logout page of each portal then also it is not working.

I have tried a lot to destroy default cookie but not working in any case.

please give some suggestion how handle such a situation.

Thanks