The ML Cache field displays the <used size / max. size> of the Image Processing Cache, and the percent of memory in use.

The Image Processing Cache Size in MB can be set in Preferences → General → Resources, see Section 4.3.1, “Preferences — General”.

To clear the image cache of all ML modules in the currently opened networks, select Extras → Clear Image Cache, see Section 4.6.12, “Clear Image Cache”.

These options can also be accessed from a context menu on this area.