Thomas:
As long as the master has control over the SCL and SDA lines it is always possible to "reset" all devices on the I²C bus by asserting a START followed by a STOP. The problem comes in when one device was left in a multi-byte read sequence and the first bit out of the hung device is a zero wherein the hung device is outputting a low on the SDA line. This causes the master to not be able to so the START / STOP type reset until the hung slave has been clocked through wayward its cycle.
Michael Karas