Create new column based on matches in another table

Question

I have 2 data frames that look something like this (it is a count table). data1 has a column called "Method" that I would like to add into data2. I want to match it based on ONLY Col1, Col2, Col3 (the Count column doesn't need to match). If there is a match, take the Method from data1 and put it in data2. If there is no match, then make the value "Not Determined". I have an example of what I'm looking for in the data frame below called data_final.

data1 <- data.frame("Col1" = c("ABC", "ABC", "EFG", "XYZ"), "Col2" = c("AA", "AA", 
"AA", "BB"), "Col3" = c("Al", "B", "Al", "Al"), "Count" = c(1, 4, 6, 2), "Method" = 
c("Sample", "Dry", "Sample", "Sample"))

data2 <- data.frame("Col1" = c("ABC", "ABC", "ABC", "EFG", "XYZ", "XYZ"), "Col2" = 
c("AA", "AA","CC", "AA", "BB", "CC"), "Col3" = c("Al", "B", "C", "Al", "Al", "C"), 
"Count" = c(1, 4, 5, 6, 2, 1))

I would like to create a new data frame that looks like this with what I described above:

data_final <- data.frame("Col1" = c("ABC", "ABC", "ABC", "EFG", "XYZ", "XYZ"), "Col2" 
= c("AA", "AA","CC", "AA", "BB", "CC"), "Col3" = c("Al", "B", "C", "Al", "Al", "C"), 
"Count" = c(1, 4, 5, 6, 2, 1), "Method" = c("Sample", "Dry", "Not Determined", 
"Sample", "Sample", "Not Determined"))

Thank you for your help!