I would rather see metacognitive techniques as tools in a toolbox. A student might be shown how to use them in a certain context then decide to try them out in a different context.
The word scaffold would seem to imply a slightly different meaning, such as the minimal instruction approach in constructivism.
An example of a metacognitive technique is the principle of parsimony.
The way I see Metacognition is from the following, the learner has self-awareness and understanding when there are engaged within a learning activity. It is like what Peter Subash points out more of a 'toolbox' to assist the learner.
I've used metacognition within web-based platforms and the use of Twitter.
The use of Twitter will enable students to develop “metacognition, forcing users to be brief and to the point” enabling them to work on descriptive and communication skills.