If you are using Drupal Console (and let's face it, why not?) then you can use:

drupal image:styles:flush image_style

Or

drupal image:styles:flush image_style

Documenation: https://docs.drupalconsole.com/en/commands/image-styles-flush.html

If you are using Drupal Console (and let's face it, why not?) then you can use:

drupal image:styles:flush image_style

Or

drupal isf image_style

Documentation: https://drupalconsole.com/docs/ca/commands/image-styles-flush