HI Sagar
As of my knowledge cache part of memory which is use to speed up the execution of a process in a short time.Hope there no ways to store reports in a cache but by default system only stores frequently accessed data in a cache,manually we cant change cache data.
If you are opening single report again and again cache will utilised,if we opened reports in a random manner because of less cache memory availability it might take mode time.
Thanks
Dipsy K