Hellbound Wither

public class SpawnBinder {

    @SubscribeEvent
    public void Wither(EntityJoinWorldEvent event)
    {
        World world = event.getWorld();
        if(event.getEntity() instanceof EntityWither && world.isRemote)
        {
            if(!world.equals(event.getWorld().getWorldInfo().getDimensionData(DimensionType.NETHER)))
                {
                    event.setCanceled(true);
                }
        }
    }
}