help needed: passing toggle signals cross clock domain

The cascade of two FF recommendation is considering the rare condition of metastable states, for most designs single FF synchronizers are sufficient to my opinion.

There may be however a problem with multibit signals (e. g. representing a number) which have to be transmitted coherently across the clock domain border. These signals need either gray encoding or you have to establish a handshake to avoid inconsistent results. Otherwise, if you have a 4-bit value changing from 0x7 to 0x8, it may be read also as 0x0 or 0xf due to delay skew.