Bro my M8 had dust the other time and I just used the wet swap to clean the sensor. Be careful not to touch the grease at the side. Once grease gets transferred to the sensor, it will never be able to clean completely. It happened on my Canon before and I hated it.
I will try to use a blower first to see if you can remove the dust. Dust of this size should be easily blown off.
Bro, shoot ISO100, f22 or whatever lowest... Either @ a clear blue sky or a white piece of paper. Any dust you will see. Minor dust will not be a concern bro...
u can always ''heal'' or ''clone'' away the spot and is not obvious unless u run from f13-f22 onwards.... my dslr have the same prob...canon guy can never clean away fully..the more u clean the more u scare scratch the sensor...sorry i am not a RF guy yet, maybe RF behaves differently..
why not run a test with white paper like what ZoomP suggest. then you will see all your dust spot