In PSSM/CSM implement, how to guarantee the whole shadow casters in the scene in the calcuated splitted light frustums?

Question

I have implemented the PSSM/CSM shadow map.PSSM/CSM use the current camera's frustum to calculate the splitted light frustums, and so improved the shadow quality, especially to casters near current camera.but casters which out of current camera's frustum may also be clipped by the splitted light frustums. we can use the whole scene to calcuate the splitted light frustums, but the shadow quality is also reduced.I have no ideas of that. How do you guys deal with this issue?