[Dovecot] How to rebuild index?

[Max Ivanov]

I've deleted some mails using my handmade tool, it deletes some files
in "cur" subdir, but deleted messages are still appear in thunderbird.
I believe that's because of stale index file. Is it safe to delete
dovect.index? Or what else should I delete/modify to make TB view in
sync with real state of filesystem?