private void broadcast(org.xmpp.packet.Roster roster) {
        JID recipient = XMPPServer.getInstance().createJID(username, null, true);
        roster.setTo(recipient);

        // When roster versioning is enabled, the server MUST include
        // the updated roster version with each roster push.
        if (RosterManager.isRosterVersioningEnabled()) {
            roster.getChildElement().addAttribute("ver", getVersion() );
        }
        SessionManager.getInstance().userBroadcast(username, roster);
    }
Returns the list of users that belong ONLY to a shared group of this user. If the contact
belongs to the personal roster and a shared group then it wont' be included in the answer.

@param sharedGroups the shared groups of this user.
@return the list of users that belong ONLY to a shared group of this user.
xmppserver/src/main/java/org/jivesoftware/openfire/roster/Roster.java