No, unfortunately, there is no active means to prohibit access within a script or within a running script in the controller or Performance Center. The best approach is to ensure that you only hit URLs assigned to your test environment and then make sure that the back end servers are properly assigned to the correct servers prior to testing. Having a good test plan and established protocols for inter-system communications is essential in any testing or development environment. Make sure that you include these in your test plan or some other form of system documentation.