Side effect of synchronous_commit = off

I was wondering whether setting synchronous_commit = off will have the following side effect.

(1) Process A issues UPDATE command on row x, from false to true.
(2) After that, Process B READ from row x.

Is it possible that when Process B start to read row x, the "true" value is not being "flushed" to the table. Hence,
processB will read the row x as false? 

If this situation will happen, is it possible that Process B may issues a command, use to "flush all" pending data to
bewritten to disk? 

Thanks and Regards
Yan Cheng CHEOK