Measuring document cluster cohesion
The Silhouette Coefficient is a good option. The Calinski-Harabaz Index has been shown to be unstable for evaluating noisy datsets, so I would recommend the Silhouette Coefficient over Calinski-Harabaz Index.  

The Clustering Validation index based on Nearest Neighbors (CVNN) index has been demonstrated to work well for many different datasets containing high noise, arbitrarily shaped clusters, and skewed distributions.

A few other validation measures you can try using are the SD validity index, the S_Dbw validitiy index, and the Xie-Beni index. 

The following is a good manuscript for interal clustering validation metrics manuscript.