Mesaana implores Moridin for help in rescuing Semirhage. She states, "We haven't the resources" to attempt a rescue. From this simple statement we learn several things.

First, Demandred is not controlling the black tower. If he was, then he would have the resources needed (i.e. channelers) to launch an attack against Rand and try to rescue Semirhage.

Second, Moridin does have access to channelers. This pretty much confirms that Moridin is running events at the black tower through Mazrim Taim.

Third, Demandred is not controlling the Seanchan or the Sharans. There have been some theories out there that both Semirhage and Demandred were controlling the Seanchan. These theories should be dispelled now. If Demandred had control of the Seanchan then he would have the resources (e.g. damane) to attempt a rescue. Similarly, if Demandred was controlling the Sharans, he would have access to their channelers. This clearly shows Demandred is not set up in Shara.

The only possibilities left for Demandred have been thought of by everyone else. Either Demandred has Murandy in his control (this is what I believe is true) or else he really does have the borderlanders in his grasp (a possibility, but less likely in my opinion).