Meaning: If you send someone to Coventry, you refuse to talk to them or co-operate with them.

It means to ignore and refuse to talk to a person.
Coventry is an industrial city in Warwickshire, England. It is well-known for its two cathedrals; the modern cathedral being built in 1962 to replace the old cathedral, which had been destroyed during an intense German bombing raid 1940.
This phrase was common in industrial disputes in Britain in the mid-twentieth century. Anyone who was considered to be unsupportive of the workforce was in danger of finding that his/her workmates refused to acknowledge their existence. Co-incidentally this was centred on the highly unionized car industry and especially British Leyland, which was largely based in Coventry. That gave rise to people who had in fact lived and worked in Coventry all their life being sent there figuratively by their workmates.