The Chinese magazine Weiqi Tiandi is possibly the best go magazine around at present, at least for strong players. Apart from being thick, well produced and varied, it offers frequent articles on go theory of a depth rarely seen before or elsewhere. Perhaps this is a reflection of the Chinese pro system. Rather than studying for years in a small group under a single teacher, they opt for large training groups with several teachers. Since entry into a squad is strictly on current merit, there can be considerable turnover in the membership of the squads. Knowledge thus gets diffused fairly quickly.
But another characteristic exists. The Chinese fret rather a lot about international success, and so the training squads examine Japanese and Korean games passionately.
Wang Xi may be considered a product of this training squad system. At the time of writing he has just crept into the top ten list of Chinese players on both the ELO and the prizewinnings charts. He is also considered to be one of the brainiest of the Chinese players.
In a recent long article in Weiqi Tiandi he gave an interview in which he listed his ten strategies for dealing with orphan groups. Each was designated by a single character, so that the ten strategies can be rattled off mnemonically by means of a little jingle.
The one we are concerned with here is xi 
which normally means 'wash'. It can be used metaphorically though,
through an extension of its meaning: rinse out >> sack a city. The go usage is
the metaphorical one, and appears to have become a bit of a vogue word among pros.
Wang Xi has brought it to the amateur audience.
The strategy denoted is to handle an orphan group not by running away but by invading even more deeply. The goal is to live, of course, and the result will be that you have sacked the opponent's city.