Lets say I have a labeled dataset to be clustered (label is to identify each data to which cluster it belongs too). Now if I used any clustering algorithm in Matlab (kmeans,...) how could I know if an instance is clustered correctly or not. 
Knowing that lets say kmeans clustered instance one of the dataset to be in clusters 2 but the labeled data says that it belongs to cluster 1. However, cluster 2 in the labeled dataset could be the same as cluster one in the predicted labels (but have different **reversed** names in both predicted and Labeled). What do you suggest?

Thank you in advance.