sdk/src/com/socialize/facebook/Facebook.java
public String logout(Context context)
            throws MalformedURLException, IOException {
        Util.clearCookies(context);
        Bundle b = new Bundle();
        b.putString("method", "auth.expireSession");
        String response = request(b);
        setAccessToken(null);
        setAccessExpires(0);
        return response;
    }
public String logout(Context context)
            throws MalformedURLException, IOException {
        Util.clearCookies(context);
        Bundle b = new Bundle();
        b.putString("method", "auth.expireSession");
        String response = request(b);
        setAccessToken(null);
        setAccessExpires(0);
        return response;
    }
Invalidate the current user session by removing the access token in
memory, clearing the browser cookie, and calling auth.expireSession
through the API.

Note that this method blocks waiting for a network response, so do not
call it in a UI thread.

@param context
The Android context in which the logout should be called: it
should be the same context in which the login occurred in
order to clear any stored cookies
@throws IOException
@throws MalformedURLException
@return JSON string representation of the auth.expireSession response
("true" if successful)