I presume from your picture you are referencing the gap between the bench top and the tiles in the corner? Have you tried using an old tooth brush or something with bristles that will get down inside the joint? An option to solve this issue going forward would be to run a bead of wet area silicone sealant along that gap to prevent the mould from entering. Any small gaps like this a notorious for building up soap scum, mould and are hard to clean.
If you need further advice on how to seal the gap with silicone, please let me know.