Boston police said Thursday that officers have swept South Boston as part of an operation to cut the flow of drugs into the community, targeting 93 people with outstanding warrants for drug offenses and property crimes. The department said that the campaign is dubbed “Operation Three Ring,” and that dozens of arrests were made from April 16 to June 12. In late April, police responded to concerned residents by vowing to crack down on the South Boston drug trade, two weeks after 67-year-old Barbara Coyne was killed in her home, allegedly by an addict.