"역시" has a veriety of meanings.
First of all, it means "also" or "too"
Second, it means "still"
Third, it means "after all"
but we often use "역시" in a sentence such as,
"(역시) 그럴줄 알았어", which means "I knew it"
"(역시) 네가 해낼줄 알았어", which means " I knew it you could make it."
Meanwhile, "혹시" is used for the meaning of "probably", "presumably" etc...
^^