This all comes down to how you define an invalid email. If you can build a smart list that pulls people with email addresses containing certain text strings that you deem "invalid", then you could run a recurring campaign to delete these people. You can add a step where it alerts you before a deletion as well.
My concern is that it's really hard to determine what is a genuine email and what is a fake one, but maybe someone else will have good suggestions there.
To be clear, there's nothing about that email address that makes it not emailable, except for the fact that the TLD .sohard doesn't currently exist in DNS. In theory, it could be a valid TLD in the future, there's nothing syntactically wrong with it.
There are number of services that do end-to-end email validation. (Insider's tip: many of them white-label the same 3rd-party infrastructure, they don't actually run their own servers + code.)
Due to community rules, I can't give a specific recommendation, but they all fundamentally work the same way: they make a real SMTP connection to the recipient's mailserver, if there is one, and start to send an email (but don't finish). There are interstitial layers of caching and some heuristics that differ across providers, but without this underlying step they can't do anything.
You can use these services via batch mode by uploading a separate CSV and then merging a result file back into Marketo. Or in trigger mode by calling a webhook. Be aware that some services have one-by-one rate limits that can be exceeded by Marketo webhooks; conversely the rate of webhook calls is much lower than the internal rate at which they can process a CSV.
A final note is that an email not being emailable isn't a reason to delete someone unless they've just been created in the system via form fillout, so you have to manage the lead sources accordingly.