Actualizado
Para MS SQL Server 2012 y superior
USE [master];
DECLARE @kill varchar(8000) = '';
SELECT @kill = @kill + 'kill ' + CONVERT(varchar(5), session_id) + ';'
FROM sys.dm_exec_sessions
WHERE database_id = db_id('MyDB')
EXEC(@kill);
Para MS SQL Server 2000, 2005, 2008
USE master;
DECLARE @kill varchar(8000); SET @kill = '';
SELECT @kill = @kill + 'kill ' + CONVERT(varchar(5), spid) + ';'
FROM master..sysprocesses
WHERE dbid = db_id('MyDB')
EXEC(@kill);