Hi,
Welcome to Adobe Community !!
"Clear Image Cache" remove the cache images files from the Dynamic Media Classic Desktop app (created on your computer), specifically when you are not getting the updated thumbnail of an uploaded image.
"Clear Asset Cache" remove the cache files (images, videos and other supported formats) from the Dynamic Media Classic Desktop app (created on your computer), specifically when you do not see upload files or folder on the user interface, even after upload job is finished.
Thanks,
Vikram Gaur