How do I delete a record in IP Cache?

Hello.

I need to delete a record in IPCache, because the ip of the given host
changed. I don't know how to update this record.

OR

How do I make squid to make dns_lookup again, so that it can update the
record?

I thought setting positive_dns_ttl as low as possible would help.
But ttl field in Ipcache stats shows relatively high values?

I must be wrong to think these are the same values.

Thanks in advance,
Anar Babayev.