Can you tell me exactly what "cache" you want to refresh? In your screenshots, I just see two images PNG and SVG and that's it. I don't know what the problem is ... Do you mean that you have already changed permissions for both files, but the gallery still shows 0644 permissions for one of the images?
Interestingly, in your top screenshot, it says 0644 which is the same as rw-r--r-- ... However, when it's RED color, it means Files gallery has checked that it is NOT writeable at the time. Seems like there was a difference between owner of the files?
Files gallery uses modified time of the folder to calculate cache. If the folder mtime did not change, it may use cache from previous visit. This should normally be automated, but you could always force cache to refresh by renaming a file in the folder or running linux command touch path/folder, updating it's modified time.
