During Invalidation sometime it becomes very difficult to hunt for non-patent references on Google. As Google provide results based on the page rank.
A very good technique to avoid this problem is by using Timeline View from Google Experimental Lab.

You need to go to Experimental Lab of Google and join the Timeline view experiment. Thereafter, all the search that you will conduct on Google will be performed under this experiment.

Advantages:
Good tool in Patentability and Invalidations
Good tool for conducting market analysis for a patent
Good tool for identifying the growth in a particular technology
Good tool for learning about history of a particular invention/product
Good tool for identifying the lauch of a particular product
A timeline chart showing the growth or drop in number of results
Please note that the results shown under a particular year in the chart doesn’t implies that they were published in that particular year. For example, the result talking about a technology in 1995 doesn’t implies that reference was published in 1995. But it provides enough hints to modify the future search to reach the exact reference for that particular year.