[boost] Boost Threading Shared Memory

I have a question regarding Boost threads, and am awaiting acceptance into the Boost Threads forum. I was wondering if anyone can help me. I am creating a multithreaded application using Boost threading, and would like to know how shared memory is implemented by Boost for threading. Each thread creates an object separately, and that object has a private member variable. We are seeing in our application that that member variable is looking the same, as if it was shared among the threads. Is this plausible? How does it work? Thanks.