purge sync. replication folder

[Patrice]

Hello,

I have seen that the folder  sync.  on my replica contains more than 1Go 
of files.
can I delete all the content of it or I must keep the current day with 
its cache file ?
I can do it with or without the replica stopped ?

I use the cyrus-imap 2.3.1


thanks in advance

Patrice