"They beat up the wife and sister of the caretaker before they started digging part of the garden ostensibly in search of weapons."
Wayne Bvudzijena, a police spokesman, had no immediate comment, The Associated Press news agency reported.
The raid came just over a week after the MDC announced it would boycott cabinet meetings with the Zanu-PF party of Robert Mugabe, Zimbabwe's president, its partner in the unity government.
Tsvangirai has said he has not quit the government, but will resume unity relations only once issues - including disputes over key posts and a crackdown against his supporters - are settled.
Biti blamed Friday's raid on members of Zanu-PF and security forces opposed to the unity government.
"We regard this as further evidence of lack of a paradigm shift on the part of Zanu-PF to treat us as an equal partner," he said.
"We regard it as serious evidence of a few in Zanu-PF and 'securocrats' who want us out of the government."
Political tensions in Zimbabwe have also been heightened by the renewed detention of Roy Bennett, a white aide to Tsvangirai, on "terrorism" charges.
Bennett is is due to go on trial on November 9.