Cache content is cleaned up automatically as needed based on time last used and a minimum age (which can be configured, see https://learn.microsoft.com/en-us/mem/configmgr/core/clients/deploy/about-client-settings#minimum-duration-before-cached-content-can-be-removed-minutes).
For Peer cache sources, you should increase the size the cache on those systems, use a task sequence and the SMSTSPreserveContent variable, or individually mark content to persist in the client's cache.
See https://learn.microsoft.com/en-us/mem/configmgr/core/plan-design/hierarchy/client-peer-cache#guidance-for-cache-management for further details.